1. Field of the Invention
The present invention relates to an apparatus for feeding printed products to a processing unit. The apparatus includes a rotating conveyor drum which individually pulls the stacked printed products from a magazine; the conveyor drum has on an approximately circular travel path, against which the printed product partially lifted from the stack by means of a separating device can be placed with an edge to be grasped, a gripping device formed by at least one movable gripping arm for receiving the printed product from the separating device, wherein the gripping device can be controlled into an open position or closed position by means of a cam mechanism connected to a closed guide track arranged in a vertical plane relative to the axis of rotation and stationary relative to the axis of rotation.
2. Description of the Related Art
CH-A-408 065 disclosed a so-called feeding machine of the type described above for a saddle stitcher in which two auxiliary gripping drums for opening the printed products are arranged downstream of the conveyor drum. The conveyor drum is formed by two drum disks which are spaced apart from each other at the axis of rotation, wherein a stationary control cam disk is arranged between the two drum disks. A gripping lever mounted between the drum disk on a shaft arranged eccentrically relative to the axis of rotation of the conveyor drum has at the outer end thereof a gripping member which interacts with the circumference of the drum disk, while at the inner end of the gripping lever is arranged a sensor roller which rests against the control cam disk under the influence of a tension spring connected to the gripping lever. A suction member is pivotably mounted parallel to the axis of rotation of the conveyor drum at the front edge of the stack of printed products; the suction member is connected to a suction pump. By means of an additional control disk connected to the conveyor drum, the suction member is pivoted upwardly once during each rotation of the conveyor drum to the lowermost sheet of the stack and after grasping the back fold edge the suction member is pivoted back, so that the back fold edge can be grasped by the gripping member and can be pulled out from under the stack.
In another embodiment of a feeder for decollating stacked printed products known in the art, a gripping arm of the conveyor drum interacting with a drum disk is actuated by a pivotable tooth segment connected to and driven by a closed guide track arranged around the axis of rotation of the conveyor drum, wherein the toothed segment engages in a pinion to which the angle-shaped gripping arm is fastened. The partial circle radius of the toothed segment is greater by a multiple than the partial circle radius of the pinion, so that a great step-down ratio is produced which results in a large opening angle of the gripping member, so that in the open position the gripping member stands back relative to the circumference of the drum disk against which the printed products rest.
The closing force to be applied by the gripping arm and the relatively high acceleration and decelerating torques resulting from the closing and opening movements of the gripping arm, which are particularly noticeable in an embodiment with toothed segment and pinion, result in substantial wear and noise phenomena which occur especially in the area of the elements used for moving the gripping arm. When these problems are to be eliminated, additional work has to be performed which results in interruptions and increased costs.
In a similar feeder for printed sheets in accordance with CH-A-641 112, a gripping drum is arranged between two lateral drum disks of the conveyor drum. A swivel shaft is rotatably mounted on the gripping drum parallel to the axis of rotation of the conveyor drum, wherein two laterally spaced apart gripping levers are rigidly attached to the swivel shaft. A pinion is mounted between the gripping levers on the swivel shaft by means of a key. Also mounted so as to be pivotable on the swivel shaft are anvil levers which interact with the gripping levers and form together with the gripping levers a gripping device. When the anvil levers travel past a folded printed sheet edge pulled downwardly by a suction device, the gripping levers are pivoted toward the swung-out anvil lever, the printed sheet edge is grasped and the printed sheet is pulled out from under the stack. The gripping levers are actuated through the swivel shaft and the pinion by a toothed segment which is rigidly attached to a control shaft. The control shaft is rotatably mounted in the gripping drum and the two drum disks and has a cam lever which engages with a cam roller in a control groove of a stationary cam disk.